Hydraulic valves are frequently used for controlling the speed and direction of operation of a hydraulic device attached thereto. Such valves include those of the spool and sliding plate type, both of which are usually operated using linear motion. Other types of such valves use rotary motion either directly or by translating linear motion into rotary motion. Examples of such valves of the latter type are shown in U.S. Pat. Nos. 4,595,034; 3,910,311 and 4,281,684. All of the foregoing typically meter fluid to the hydraulic device solely by the gradual intersection of two ports or passages and are devoid of any load sensing capability.
In general, valves of the spool and slide plate type achieve balance of the valving member by closely controlling the dimensions of the valving member and of the cavity in which it moves. Fluid at a substantially uniform pressure is permitted to surround the valving element and results in what might be called a natural balancing arrangement. Valves which use a rotary principal of operation either achieve balancing in a similar fashion as described above (see U.S. Pat. No. 4,281,684, for example) or, in the alternative, employ no special structure to achieve balancing. Instead, the rotary valving plate is held in position mechanically rather than with hydraulic pressure An example of such a valve is shown in U.S. Pat. No. 4,595,034.
Known rotary valves of the foregoing type lack what is known as a "meter in" capability. That is, they include no provision for metering fluid into the valve structure prior to the introduction of such fluid to the valving face and the working ports of the device being controlled. In addition, designers of such earlier valves have failed to appreciate the way in which a separate flow sensor may be integrated into and used with a rotary valve to permit incoming hydraulic fluid to partially or substantially entirely bypass the valving portion of the device and be routed to tank at the line side.
Another factor to be addressed by a valve designer is that of "packaging" of auxiliary hydraulic circuit components into a directional valve including such a valve of the rotary type. Such components include relief valves and flow control valves, to name but a few. While the packaged integration of these components into a directional valve tends to make the latter more expensive to purchase, this cost is more than offset by the ease of installation of the valve into the overall hydraulic circuit. That is, the installer need not separately purchase, mount and attach piping and hoses to such auxiliary valves. U.S. Pat. No. 4,595,034 shows one approach to packaging such auxiliary valves. The apparatus shown therein includes a built-in relief valve connected on the load side of the valve rather than on the incoming or line side thereof.
In addition, applications are encountered where it is highly desirable to retain the rotated position of the valve while yet causing hydraulic fluid to bypass the internal valving surfaces and instead, be routed to the discharge port. Such a feature permits the controlled device, a motor for example, to be temporarily stopped without the necessity of manipulating and later resetting the position of the valving surfaces.
A rotary hydraulic valve which uses a face plate with a controlled degree of imbalance, which uses an axially arranged infeed circuit having a "meter in" capability, which provides both direction and speed control with rotational movement and which integrates auxiliary valving to perform specialty control functions would be an important advance in the art.